Propagation growth of en echelon detachment folds: Case from the Nankalayuergun fold zone, North Tarim Basin, NW China

Abstract

The Nankalayuergun fold zone in the North Tarim Basin, NW China, provides an exceptional opportunity for documenting the structural characteristics and evolution of en echelon folds that are associated with strike-slip faults. Seismic, borehole, and gravity data show that en echelon folds are geometrically decoupled by salt structures and that the structural styles of salt-influenced anticlines have distinct characteristics due to differences in salt thicknesses. The timing and amplitude of the Cenozoic evolution of the folds occurred sequentially from NW to SE, indicating progressive deformation. In contrast to classic en echelon structures, the supra-salt folds are only located on the active sides of the multi-segment Deep Nankalayuergun Fault (DNF). The structural relief of the supra-salt folds is the sum of the detachment and sub-salt folds, indicating kinematic coupling. The supra-salt fold axes are located directly above the sub-salt monoclines, corresponding to the reactivation of the DNF. The dextral transpressional regime, pre-existing structures, and salt rock heterogeneities are major factors that form the stratified and polygenetic folds. The case and method (structural relief analysis) presented in this study highlight the influences of pre-existing structures and can be used to interpret similar structures that have undergone stratigraphically decoupled deformation.